diff --git a/trl/trainer/callbacks.py b/trl/trainer/callbacks.py
index a530e38b0c4..9885c872d97 100644
--- a/trl/trainer/callbacks.py
+++ b/trl/trainer/callbacks.py
@@ -66,6 +66,7 @@ def _generate_completions(
     accelerator: Accelerator,
     generation_config: GenerationConfig | None,
     batch_size: int = 1,
+    **generation_kwargs,
 ) -> list[str]:
     """
     Generates completions for a list of pre-formatted prompts from the given model.
@@ -77,12 +78,14 @@ def _generate_completions(
         accelerator (Accelerator): The accelerator to be used for model execution.
         generation_config (GenerationConfig): Configuration for text generation.
         batch_size (int, optional): The number of prompts to process in each batch. Default is 1.
+        **generation_kwargs: Additional keyword arguments forwarded to `model.generate`. These
+            override any matching fields in `generation_config` (e.g. `max_new_tokens=50`,
+            `temperature=0.8`).
 
     Returns:
         list[str]: A list of generated text completions corresponding to the input prompts.
     """
     completions = []
-    # TODO: Override model.generation_config with generation_kwargs
     with unwrap_model_for_generation(model, accelerator) as unwrapped_model:
         for idx in range(0, len(prompts), batch_size):
             batch = prompts[idx : idx + batch_size]
@@ -90,6 +93,7 @@ def _generate_completions(
             generations = unwrapped_model.generate(
                 **tokenized_batch,
                 generation_config=generation_config,
+                **generation_kwargs,
             )
             for prompt, generation in zip(tokenized_batch.input_ids, generations, strict=True):
                 # Remove prompt from generation
@@ -258,7 +262,7 @@ class LogCompletionsCallback(TrainerCallback):
     Usage:
     ```python
     trainer = DPOTrainer(...)
-    completions_callback = LogCompletionsCallback(trainer=trainer)
+    completions_callback = LogCompletionsCallback(trainer=trainer, max_new_tokens=50)
     trainer.add_callback(completions_callback)
     ```
 
@@ -273,6 +277,9 @@ class LogCompletionsCallback(TrainerCallback):
             the evaluation dataset.
         freq (`int`, *optional*):
             The frequency at which to log completions. If not provided, defaults to the trainer's `eval_steps`.
+        **generation_kwargs:
+            Additional keyword arguments forwarded to `model.generate`. These override any matching fields in
+            `generation_config` (e.g. `max_new_tokens=50`, `temperature=0.8`).
     """
 
     def __init__(
@@ -281,9 +288,11 @@ def __init__(
         generation_config: GenerationConfig | None = None,
         num_prompts: int | None = None,
         freq: int | None = None,
+        **generation_kwargs,
     ):
         self.trainer = trainer
         self.generation_config = generation_config
+        self.generation_kwargs = generation_kwargs
         self.freq = freq
         self.table = []
         self._last_logged_step = -1
@@ -319,6 +328,7 @@ def on_step_end(self, args, state, control, **kwargs):
                 accelerator=accelerator,
                 generation_config=self.generation_config,
                 batch_size=args.per_device_eval_batch_size,
+                **self.generation_kwargs,
             )
             completions = gather_object(completions)
             prompts = gather_object(prompts)
@@ -405,6 +415,9 @@ def accuracy_scorer(prompt: str, completion: str) -> float:
             Name for the dataset metadata in Weave.
         model_name (`str`, *optional*):
             Name for the model metadata in Weave. If not provided, attempts to extract from model config.
+        **generation_kwargs:
+            Additional keyword arguments forwarded to `model.generate`. These override any matching fields in
+            `generation_config` (e.g. `max_new_tokens=50`, `temperature=0.8`).
     """
 
     def __init__(
@@ -416,11 +429,13 @@ def __init__(
         num_prompts: int | None = None,
         dataset_name: str = "eval_dataset",
         model_name: str | None = None,
+        **generation_kwargs,
     ):
         self.trainer = trainer
         self.project_name = project_name
         self.scorers = scorers or {}
         self.generation_config = generation_config
+        self.generation_kwargs = generation_kwargs
         self.dataset_name = dataset_name
         self.model_name = model_name
         self._last_logged_step = -1
@@ -503,6 +518,7 @@ def on_evaluate(self, args, state, control, **kwargs):
                 accelerator=accelerator,
                 generation_config=self.generation_config,
                 batch_size=args.per_device_eval_batch_size,
+                **self.generation_kwargs,
             )
 
             all_prompts = gather_object(prompts)
@@ -513,6 +529,7 @@ def on_evaluate(self, args, state, control, **kwargs):
                 "training_step": state.global_step,
                 "model_name": self.model_name,
                 "generation_config": (self.generation_config.to_dict() if self.generation_config else None),
+                "generation_kwargs": self.generation_kwargs,
             }
 
             eval_logger = self._EvaluationLogger(